Activated carbon products are commonly used in diverse industries. Activated carbon is used successfully for purification and remediation applications. Powdered activated carbons (PAC) have been used for more than 90 years to purify a wide variety of food, water and chemical products. Powdered activated carbon typically has an extraordinarily large surface area and pore volume. The particle size distribution of powdered activated carbon is typically controlled to provide combinations of fast kinetics, high capacity, good settling and suspension characteristics and low-pressure filtration in various applications. Powdered activated carbons are available in a variety of grades; they cover a range of pore size distributions, surface chemistries and purity levels. For example, powdered activated carbon can generally have a mean particle size of less than about 500 microns. Many grades of activated carbon meet the standards of the Food Chemical Codex and are certified NSF/ANSI 61 and 42. For example, Nuchar SA-20 brand powdered activated carbon (Westvaco) is commonly used in preparing carbon-containing blends with diatomaceous earth, from which certain spent carbon materials can be recovered.
Environmental applications for powdered activated carbon include potable water and odor control. Activated carbon is also commonly used to purify water containing halogenated hydrocarbons such as trihalomethane, color, chlorine/chloramine, and various man made organic compounds such as herbicides and pesticides. The removal of organic compounds from process water is commonly practiced in a wide range of industries, including chemical manufacturing and petroleum refining. The removal of free chlorine from water is a process widely used throughout the world by beverage manufacturers, industrial water treatment processors and others. Activated carbon is used when removing the total residual combined chlorine that exists after chlorination to reduce the toxic effects of chlorinated effluents discharged to receiving waters or to be used for reuse applications.
Various facilities that employ combustion or incineration processes (including municipal waste incinerators, hazardous waste incinerators, and medical waste facilities) require safe, easy, and cost-effective methods of mercury and/or dioxin control to meet strict federal regulations. Certain forms of activated carbon are used in municipal wastewater treatment, biological filters, and chemical scrubbers. Industrial process water is widely treated for the removal of free chlorine and organic compounds, and often demineralized, and disinfected.
It will be appreciated that these and other processes consume large amounts of activated carbon, especially powdered activated carbon. After use the activated carbon becomes spent carbon. Spent carbon presents issues regarding disposal, possible re-generation, and other problems. The challenges are both technological and economic.
Activated carbon sometimes has been proposed as an additive for animal litters. As a primary component to the spent carbon material, powdered carbon or activated carbon has been deemed essential to obtaining an additive capable of removing undesired odors. By itself, activated carbon is frequently undesired for use in animal litters because it tends to segregate out during shipping, thereby creating dust. Another drawback is the so-called “black paws” where an animal's paws pick up carbon particles from litter and track the carbon particles around. Efforts to incorporate activated carbon in litter by conventional granulation methods yield granules with limited surface area for absorbing odors.